Silicon particles (silicon nanoparticles) having a particle diameter of the order of nanometers have physical and chemical properties considerably different from those of bulk silicon, and are attracting a lot of attention as new functional material in recent years. For example, the silicon nanoparticles have a band structure different from that of the bulk silicon based on the quantum confinement effects and surface level effect, and a luminous phenomenon which is not observed on the bulk silicon is observed, so that it is expected to be applied as material for a novel silicon light emitting device.
Ordinary fine silicon powder obtained by finely pulverizing silicon has physical and chemical properties substantially corresponding with those of the bulk silicon. Meanwhile, the silicon nanoparticles have a very fine particle diameter, a relatively small particle size distribution width, and high purity. Therefore, it is considered that a peculiar property such as a luminous phenomenon quite different from the bulk silicon is expressed.
Conventionally, as the method for production of silicon nanoparticles, there have been used, for example, (1) a method of passing silicon vaporized by a first high-temperature plasma generated between mutually opposed silicon electrodes through a second high-temperature plasma generated by electrodeless discharge in a reduced-pressure atmosphere (Patent Literature 1), (2) a method of separating and removing silicon nanoparticles from a positive electrode, which is formed of a silicon wafer, by electrochemical etching (Patent Literature 2), and (3) a method for electrode reduction of a halogen-containing organic silicon compounds using reactive electrodes (Patent Literature 3).
But, the above-described methods (1), (2) are hard to improve productivity because they have a considerably low silicon nanoparticle generation speed. The above-described method (3) has a halogen element such as Cl in raw material, and it is easily mixed into a product, so that a total amount of Na, Fe, Al, Cl is hard to become 10 ppm or less.
Therefore, it is quite difficult to produce high-purity silicon nanoparticles which are useful as material powder for high-performance light-emitting elements and electronic parts in an industrial scale.
Meanwhile, for expression of a luminous phenomenon or the like based on the above-described band structure and surface level effect, a so-called superlattice structure that has silicon particles having a uniform particle diameter of the order of nanometers two-dimensionally or three-dimensionally arranged periodically with regularity must be formed.
Therefore, as a specific method of using the silicon particles of the order of nanometers as new functional material, there is required a method that selectively removes particles having a particular size from silicon particles produced in a large amount and arranges them two-dimensionally or three-dimensionally, or forms a superlattice.
Conventionally, as a method for production of silicon particles or a superlattice containing the silicon particles, or a film or a formed product having the silicon particles arranged, there are proposed (a) chemical vapor deposition (CVD) method (Patent Literatures 4, 5), (b) spin coat method (Patent Literature 6), (c) method of straining a suspension containing particles through a porous barrier wall to obtain particles (Patent Literature 7), (d) method of using particle electrophoresis (Patent Literature 8), and the like.
But, the above method (a) is often performed in vacuum at a high temperature or in a plasma atmosphere, so that a highly controlled vacuum heating device or a plasma generating device is necessary and the cost becomes high. And, the method (b) does not need an expensive device such as that used for the method (a) but product yield lowers considerably. The methods (c), (d) arrange particles on the porous barrier wall or electrode, but there is no appropriate method for removal of a film or formed product which is formed of a superlattice from such materials.
The superlattice containing the conventional silicon particles obtained by the above methods has variations in particle diameter, so that the band structure or the surface level becomes unstable. When it is used as a light-emitting element, luminous efficiency does not become high enough, and when it is used as electronic parts, there is a possibility of malfunction.
[Patent Literature 1] Japanese Patent Laid-Open Publication No. Hei 6-279015
[Patent Literature 2] Japanese Patent Publication No. 2003-515459
[Patent Literature 3] Japanese Patent Laid-Open Publication No. 2002-154817
[Patent Literature 4] Japanese Patent Laid-Open Publication No. Hei 5-62911
[Patent Literature 5] Japanese Patent Laid-Open Publication No. Hei 6-349744
[Patent Literature 6] Japanese Patent Laid-Open Publication No. Hei 11-1308867
[Patent Literature 7] Japanese Patent Laid-Open Publication No. 2002-279704
[Patent Literature 8] Japanese Patent Laid-Open Publication No. 2003-89896